The present invention generally relates to track-and-hold and/or sample-and-hold circuits, and more particularly to an apparatus for providing accurate track and hold functionality for a number of different input signal types.
Track-and-hold (TandH) circuits, and the more general sample-and-hold (SandH) circuits, are used in a variety of applications, such as analog-to-digital converters (ADCS) and switched capacitor filters. A conventional TandH circuit in its simplest sense includes a switch and a capacitor to first xe2x80x9ctrackxe2x80x9d the input signal, and to subsequently xe2x80x9choldxe2x80x9d the input signal for processing. The most prevalent use of TandH circuits is as a front-end for ADCS. A TandH circuit receives analog continuous-time signals, and converts them to analog sampled data signals. These analog sampled data signals can then be processed, for example, by an ADC to ultimately provide a digital representation of the original analog continuous-time signal.
A variety of different input signal types may represent the analog continuous-time signal that is to be sampled, held, and ultimately processed. For example, a single-ended signal source, such as a voltage signal across a resistance or other impedance, may provide a unipolar signal where a first input signal (e.g., VP) is always greater than or equal to a second input signal (e.g., VN) Track-and-hold circuits exist to sample and hold such unipolar signals. Different circuit architectures exist to accommodate bipolar signals, such as where the signal source is derived from a bridge or other circuit arrangement where VP can be greater than or less than VN. Still other circuit designs can accommodate differential input signals.
However, current TandH technology is geared to the particular type of input signal that is to be provided. Different circuits are therefore required to track/hold continuous-time signals from a like number of different input signal types. These existing circuits are inflexible in terms of dealing with different types of input signals.
The present invention addresses these and other shortcomings of the prior art, and provides a solution to the problems exhibited by prior art TandH and SandH circuits.
In various embodiments, the present invention provides an accurate and highly versatile track-and-hold/sample-and-hold circuit capable of operating with a plurality of different types of input signals.
In accordance with one embodiment of the invention, a track-and-hold circuit is provided that includes a pair of circuits each receiving first and second input signals and providing half of a differential output signal. The first and second input signals received by each respective circuit are reversed relative to each other, i.e., where the first circuit respectively receives InP and InN at first and second inputs, the second circuit respectively receives InN and InP at the corresponding inputs. Each of the circuits of the circuit pair includes an amplifier, and a configurable switch circuit coupled to a selected one of a plurality of selectable reference voltages based on an expected input signal type. Each circuit includes a first switched capacitor circuit to sample its respective first input signal relative to a common mode voltage in response to a first clock phase, and to couple the sampled first input signal in a feedback configuration between an output and a negative input of the amplifier in response to a second clock phase. Each circuit further includes a second switched capacitor circuit to sample its respective second input signal relative to the common mode voltage in response to the first clock phase, and to couple the sampled second input signal to a positive input of the amplifier relative to the selected one of the selectable reference voltages in response to the second clock phase. In this manner, the amplifiers of the circuit pair collectively provide the differential output signal as a differential version of the difference between the sampled first and second input signals as shifted by the selected one of the selectable reference voltages. The circuit is operational with a variety of different input signal types, including unipolar signals, bipolar signals, and differential input signals.
It will be appreciated that various other embodiments are set forth in the Detailed Description and Claims which follow.